Users of portable battery powered communication devices are dependent on a fully functional device. More specifically, the users need to know exactly for how long their devices will remain functional, until the electrical energy stored in the battery has been consumed and the battery has to be recharged. This is particularly true for users of mobile telephones.
In order to determine a precise estimation of the remaining operational time of a mobile telephone, the user needs an accurate and well functioning battery capacity indicator or “fuel gauge”. Determining the remaining battery capacity includes two separate current measurements One measurement from the current flowing into the battery “charging” and one measurement for the current consumed from the battery “discharging”. The charging current is often relatively easy to measure. A microprocessor “CPU” may determine the current signal which is directly proportional to the current flowing through a small resistor. Since a microprocessor controls the charging process, it will also have access to all relative data for calculating the total energy, that has been supplied to the battery during a certain period of time.
Determining the discharge current or current consumption is much more difficult, particularly for advanced telephones with complex functionalities and many operating modes. Traditionally, discharged current is measured by calculating the expected current consumption, when the telephone is in different operating modes. Earlier mobile telephones basically had two operating modes, talk mode and standby mode. With such telephones, the current consumption for talk modes and standby modes was measured once in a test laboratory environment and stored in memory in the telephone as respective, predetermined consumption values. In operation, the telephone would keep track of the time spent in talk mode and standby modes and subsequently calculate the total amount of energy consumed within the battery by multiplying the respective operational times by the predetermined consumption values.
Recently it has been possible to use application specific integrated circuits (ASICS) to measure current flowing in and out of a battery. To be able to predict remaining operating time, existing mobile telephones are required to track how each setting of the mobile telephone sets current consumption from a battery. The added current consumption for each setting must be measured in a lab and stored within the mobile telephone's non-volatile memory at production. The software in the mobile telephone is configured to consider the different menu settings when calculating remaining operating time for the battery. Additionally, the mobile telephone must track activities towards the network within various modes such as standby and call. This could be done by counting the number of RX, TX and SYNT strobes in the different modes of telephone. Each strobe contains a certain amount of energy that is measured in the lab and stored as a parameter in the non-volatile memory. These networks activities must be included when estimating the current power consumed in each mode of the mobile telephone.
These methods, however, are quite complex to use in practice due to the large amount of measurements that must be done in the lab, and the large amount of data that must be stored in the mobile phone. Each increases the complexity and cost associated with a mobile telephone